Speed Of Sound
The speed of propagation of a sound wave is dependent upon the density of the medium of transmission. Weather conditions (e.g., temperature, pressure, humidity, etc.) and certain geophysical topographical features (e.g., mountains or hills) can obstruct sound transmission. The alteration of sound waves by commonly encountered meteorological conditions is generally negligible except when the sound waves propagate over long distances or emanate from a high frequency source. In the extreme cases, atmospheric conditions can bend or alter sound wave transmission.
The speed of sound on a fluid—inclusive in this definition of "fluid" are atmospheric gases—depends upon the temperature and density of the fluid. Sound waves travel fast at higher temperatures and density. As a result, in a standard atmosphere, the speed of sound (reflected in the Mach number) lowers with increasing altitude.
Meteorological conditions that create layers of air at dramatically different temperatures can refract sound waves.
The speed of sound in water is approximately four times faster than the speed of sound in air. SONAR sounding of ocean terrains is a common tool of oceanographers. Properties such as pressure, temperature, and salinity also affect the speed of sound in water.
Because sound travels so well under water, many marine biologists argue that the introduction of man-made noise (e.g., engine noise, propeller cavitations, etc) into the oceans within the last two centuries interferes with previously evolutionarily well-adapted methods of sound communication between marine animals. For example, man-made noise has been demonstrated to interfere with long-range communications of whales. Although the long term implications of this interference is not fully understood, many marine biologists fear that this interference could impact whale mating and lead to further population reductions or extinction.
Deutsch, Diana. Ear and Brain: How We Make Sense of Sounds. New York: Copernicus Books, 2003.
Rossing, Thomas D., F. Richard Moore, Paul A. Wheeler. The Science of Sound. 3rd ed. Prentice Hall, 2001.